Note: This bug is in the Japanese version only. Please refer to the SM64: From Japanese to English page for more details.

While fighting Bowser in "Bowser in the Dark World," avoid his fire breath and keep picking up the coins that come from the flames. When you reach a total of 1,000 coins in the level, your extra life total will change to M25. You can think of the "M" as a minus sign, because your extra life total will act as though it's a negative number. That is, your total will go down when you'd normally gain a life, and it will go up when you'd normally lose a life. For instance, if you threw yourself off of Bowser's platform with M25 lives, you'll return with M26 lives in reserve.

It should be noted that if you defeated Bowser or exited his stage via the pause menu after getting the "M," neither 1-Ups nor deaths will affect your lives total until you enter a stage again. With that in mind, talking to Yoshi at this point will "lock up" the game. He'll try to give you 100 lives, but your extra life total won't move, and you'll be stuck on the roof with Yoshi while the "counting" sound effect keeps playing.

Mario can lose the "M" in two ways. If you get enough 1-Ups to bring your extra life total down to M1, the next 1-Up you get will change the total to 0, and the "M" will go away. If you die enough to bring your lives up to M128, the "M" will go away the next time you lose a life, and the extra life total will change to 100. A quick way to lose the "M" is to talk to Yoshi—even if you have M128 lives, your total will count down to 0 (that's when you'll lose the "M") and then count up to 100 "normal" lives in reserve.